In a flip-chip type assembly mounting electronic parts, it is necessary to alleviate the stress generated between the devices and the substrate. Now, there are various structures for alleviating the stress to the devices.
FIG. 1 shows a conventional flip-chip type-assembly. In order to realize high-speed operation, a bare LSI 2 is used instead of a packaged LSI. A substrate 1 may be an organic substrate. FIG. 1 shows the bare LSI 2 mounted on the substrate 1 using a flip-chip technology.
As shown in FIG. 1, the bare LSI 2 is mounted on the substrate 1 using the flip-chip technology. Electrodes 21 on the LSI 2 are bonded to electrodes 11 on the substrate 1 by solder 6. After that, resin 5 fills space between the substrate 1 and the LSI 2. The resin 5 protects the solder 6.
Coefficients of thermal expansion of the LSI 2 and the substrate 1 are different from each other. The coefficients of thermal expansion of the LSI 2 and the substrate 1 are about 3.5 ppm/° C. and about 15 ppm/° C., respectively. Difference in the coefficients of thermal expansion causes stress. The resin 5 prevents the solder 6 from being broken by the stress. In other words, the solder 6 is protected by the resin 5. However, in a structure shown in FIG. 1, the stress is also applied to the LSI 2. As a result, the LSI 2 is bent by the stress.
An LSI which adopts an SiO2 film is strong in itself, and thus, even when stress is applied to such the LSI which adopts an Sio2 film, the LSI is not broken. However, as an LSI for realizing operation at high speed or more, an LSI using a low-k film is used. The low-k film is a film having low relative permittivity and an interlayer insulating film. Such the low-k film is weak against stress and is fragile. Since the LSI using the low-k film is liable to be broken by stress, the stress is required to be alleviated.
FIG. 2 shows a structure disclosed in Japanese Patent Application Laid-open No. Hei 11-54884. A semiconductor package includes LSI electrodes 21 and a carrier substrate 9. The carrier substrate 9 is made of ceramic. The electrodes 21 on the LSI 2 and electrodes on the carrier substrate 9 are connected by the solder 6. Further, resin 5 fills space between the LSI 2 and the carrier substrate 9. The resin 5 has insulating property. The substrate 1 has substrate 10 mounted thereon. The substrate 10 is made of ceramic. The substrate 10 is used for mounting the semiconductor package thereon. Electrodes on the substrate 10 and the electrodes 11 on the substrate 1 are connected by the solder 6. The resin 5 also fills space between the substrate 1 and the substrate 10. Further, the electrodes on the carrier substrate 9 and the electrodes on the substrate 10 are connected by the solder 6.
Here, the difference between the coefficients of thermal expansion of the ceramic as a material for the carrier substrate 9 and of the ceramic as the material for the substrate 10 is preferably 50% or less. More preferably, the ceramic as the material of the carrier substrate 9 and the ceramic as the material of the substrate 10 are the same. As a result, the coefficients of thermal expansion of the carrier substrate 9 of the semiconductor package and the package receiving substrate 10 are the same or have close values. Thus, the solder 6 is not broken by stress caused due to the difference in the coefficients of thermal expansion is solved.
FIG. 3 shows a structure disclosed in JP 2000-307025 A. The LSI 2 is bonded to an interposer 12 made of ceramic. Connecting terminals 13 are mounted on the interposer 12 on a side opposite to a side facing the LSI 2. The connecting terminals 13 are connected to the electrodes on the LSI 2. Further, the connecting terminals 13 are connected to members 14. The members 14 are formed of resin which is conductive. The members 14 alleviate stress. Metals 15 are formed on the surface of the members 14. The metals 15 can be connected through soldering.
The metals 15 have a trapezoidal shape. More specifically, the area of the metals 15 respectively connected to the members 14 is smaller than the area on the opposite side thereof. In a case of temperature rise, stress is caused due to the difference in the coefficients of thermal expansion between the interposer 12 and the substrate 1. However, since the members 14 are elastically formed, the members 14 absorb the stress. As a result, that solder is not broken.
FIG. 4 shows a structure disclosed in Japanese Patent No. 3629178. Post electrodes 16 are formed on the LSI electrodes 21. Support plates 17 are disposed around the post electrodes 16 so as not to come into contact with the post electrodes 16. The post electrodes 16 are connected to the substrate 1 by metal bumps 19. Further, the post electrodes 16 and the support plates 17 are covered with resin 18 such that only electrode portions are exposed. The post electrodes 16 are deformed under stress. As a result, stress caused due to difference in the coefficients of thermal expansion of the substrate and the LSI is alleviated.
However, in the package structure shown in FIG. 2, the stress caused due to difference in the coefficients of thermal expansion of the LSI 2 and the carrier substrate 9 is applied to the LSI. Therefore, it has little effect on alleviation of stress on the LSI 2. Strength of an LSI using a conventional SiO2 film is strong. Thus, even if stress is applied to the LSI itself, the LSI is not broken. However, since the LSI using the low-k film is fragile, there is a problem that the stress causes breakage of the LSI. Further, since the package structure shown in FIG. 2 includes many joints using solder, the number of process steps in assembling is increased. In addition, since the distance between the LSI and the substrate is large, electric characteristics are deteriorated.
Similarly, in the package structure shown in FIG. 3, thermal stress is caused between the LSI 2 and the interposer 12 because they have different coefficients of thermal expansion. The thermal stress can be absorbed or alleviated by the member 14, which is made of a resin. However, the LSI 2 cannot be detached from the substrate 1 easily by heating because the member 14 connecting them is not made of solder but resin.
In the package structure shown in FIG. 4, the post electrodes 16 are made of metal having high elasticity modulus. Therefore, it has little effect on alleviation of stress on the LSI 2. In addition, the manufacturing of the post electrodes 16 is difficult.
Incidentally, it is desirable that an LSI can be detached from the substrate without damaging itself or the substrate when only the LSI is replaced without replacing other parts on substrate. In the structures shown in FIG. 1 and FIG. 2, the LSI 2 is secured to the substrate or the interposer with the resin 5. Therefore, once the LSI 2 is mounted, it cannot be detached easily from the substrate or the interposer. In the structure shown in FIG. 3 and FIG. 4, it is difficult to detach LSI without damaging the substrate because the members connecting the LSI 2 and the substrate 1 are not solder but the resin and the metal bumps, respectively.
In the structure shown in FIG. 3, resin can be used to fill the space between the interposer and the substrate to alleviate the stress more. However, if the space between the interposer and the substrate is filled with the resin, it becomes much more difficult to detach the LSI 2 from the substrate 1. In other words, in the structure shown in FIG. 3, it is difficult to alleviate the thermal stress sufficiently while allowing the LSI 2 to be detached from the substrate 1 easily.
Accordingly, in order to solve the above-mentioned problems, the present invention provides a structure in which the stress between LSI and substrate is alleviated sufficiently, and LSI can be detached from substrate easily. The connecting member between the LSI and the interposer is removable easily by being heated. In addition, joints are reliable.